Lightwave ovens having linear sources of visible and infra-red radiant energy are disclosed and described in U.S. Pat. No. 5,036,179, which is incorporated herein by reference. These ovens provide high-speed, high-quality cooking and baking of food items by impinging high-intensity visible, near-visible, and infrared radiations onto a food item. Lightwave ovens cook the food items within the short periods of time normally found in microwave cooking while maintaining the browning of infrared cooking and the quality of conduction-convection cooking. When food is exposed to a sufficiently intense source of visible, near-visible, and infrared radiation, the food absorbs low levels of visible and near-visible radiation, thereby allowing the energy to penetrate the foodstuff and heat it deeply. The longer infrared radiation does not penetrate deeply but acts as an effective browning agent.
Ordinarily, the source of the visible, near-visible and infrared radiation is one or more quartz-halogen tungsten lamps, or equivalent means such as quartz arc lamps. Typical quartz-halogen lamps of this type convert electrical energy into black body radiation having a range of wavelengths from 0.4 .mu.m to 4.5 .mu.m with a peak intensity at approximately 1 .mu.m at an operating temperature of approximately 2898.degree. K. and a significant portion of the energy, approximately 10.6% in the visible light spectrum 0.39 to 0.77 .mu.m and approximately 7% in the visible light spectrum of 0.4 to 0.7 .mu.m. In the preferred embodiment, the lamps operate at 3000 degrees Kelvin and convert electrical energy into black body radiation having a range of wavelengths from 0.4 .mu.m to 4.5 .mu.m with a peak intensity at 0.965 .mu.m producing approximately 12% of the radiant energy in the visible range 0.39 to 0.77 .mu.m or approximately 8.1% in the visible light spectrum of 0.4 to 0.7 .mu.m of the electromagnetic spectrum. Each lamp can generally provide up to 1.5 to 2 KW of radiant energy with a significant portion of the energy in the visible light spectrum.
The ovens can use a plurality of these lamps or an array of several lamps either operated in unison or selectively operated in varying combinations as necessary for the particular food item sought to be cooked. These radiation sources are ordinarily positioned above and below the food item. The walls of the surrounding food chamber are preferably made from highly reflective surfaces. The visible and infrared waves from the radiation sources impinge directly on the food item and are also reflected off the reflective surfaces and onto the food item from many angles. This reflecting action improves uniformity of cooking.
Ovens of this type preferably include a microprocessor into which cooking times for a variety of dishes and food types may be entered. This allows the user to select the cooking time for a specific dish using controls located on the front panel of the oven. Selecting the cooking program for a specific dish will illuminate the lamps for the cooking time required to cook the specific dish.
Conventional thermal ovens cook food by transferring energy to the food and heating it by a combination of radiation and conduction and convection through the air. It is well known that virtually all conventional thermal ovens require a "preheat" time during which the temperature inside the oven is raised to the desired cooking temperature. During preheating, the air and oven walls inside the oven accumulate and store heat energy. Thus the amount of heat that must be supplied to the oven is reduced during the cooking cycle.
The cooking function in a lightwave oven is not primarily performed by the same means used in a thermal oven. Cooking is instead accomplished by the interaction of the visible light and infrared radiation with the food. In a normal cooking cycle, the food is positioned inside a room-temperature oven. The radiation sources, or lamps, are then illuminated for the duration of the cooking cycle, termed the "normal cooking time", and are immediately turned off at the end of the cooking cycle. If several separate food items are to be cooked, the process is repeated for each food item; the lamps do not remain illuminated between the cooking cycles.
Food items in lightwave ovens are cooked for predetermined periods of time, and cooking times are calculated under the assumption that ovens are initially at room temperature and are programmed into the ovens for various different food items. If several items of food are cooked in sequence, heated air accumulates in the oven and all components of the oven cavity heat up through a combination of thermal radiation and convection and conduction so that heat is transferred to the food over and above what is transferred via the lamps. This source of heating will be termed "oven secondary heating". With each consecutive cooking cycle the required cooking time thus decreases due to the accumulation of heat energy within the oven.
When the cooking cycle is timed using a radiant source oven that is initially at room temperature, the oven normally cooks a 9 inch diameter pizza in 65 seconds. If several pizzas are cooked in rapid sequence, the cooking time decreases to 45 seconds after 2 or 3 pizzas are cooked. If heat accumulation within the oven is not factored into the cooking cycle, the oven will produce pizzas that are burned.
Because the oven's internal parts become heated during cooking, evacuation of heated air cannot fully compensate for the problem of increased oven temperature. A solution is needed whereby adjustment is made for added oven energy and to compensate for an increased oven temperature.